February and March are pretty safe all over.
I would lean towards February if you are focusing on places like Revelstoke or Fernie.
March (even late March) will be better for Kicking Horse, Lake Louise, and Sunshine.
February 17, 2020 is Family day in Alberta and BC. That weekend is most likely to be busy, and accomodations will probably be expensive then too. Otherwise, resorts will be crowded if there is new snow (especially on a Saturday), but should be relatively empty otherwise. I generally ski right on to lifts unless it is a powder day. Kicking Horse doesn't handle crowds well with a huge bottleneck at the gondola (the terrain is good though). Revelstoke is a bit better than Kicking Horse, but not by much.
Early January will be cheap and not too busy. Generally speaking Revelstoke and Fernie are in their prime's in January. The Banff resorts take a bit longer to build a base.
For backcountry skiing, the snowpack in the Rockies is more reliable in the later season, and can be quite touchy in the dead of winter. Long cold periods between storms are prime for surface hoar, which then gets burred. Skiing on the icefields is more plesant later in the season as well....where you can have some confidence in the strength of snow bridges.
Most of Rogers Pass (and the Columbia Mountains in General) skis nicely throughout the winter. Rogers is busy though.
Read these books for ideas:
http://www.geobackcountry.com/book
http://confessionsofaskibum.com/2018/10/02/the-icefields-parkway-lake-louise-to-bow-summit/
Some free downloads
http://confessionsofaskibum.com/2017/01/01/citadel-to-egypt-lake-banff-backcountry-skiing/
The CaPow guys offer interesting guided trips. And you might get to ski with your ski-heros.
http://capow.ca/
I have only climbed with Brent Peters, but he is a great guide...especially good at the instruction side of things.
http://www.peakstratagem.com/
He has been doing trips out of the Boulder Hut in the Purcells lately.
If you and your girlfriend are okay with spliiting up for a day or two, I have heard rave reviews about Girls do ski camps.
https://www.girlsdoski.com/
They often do resort camps for Revelstoke or Kicking Horse